| Hevea brasiliensis is an important tropical crop and strategic material resource of our country.From 2014 to 2016,a kind of new stem canker disease was widely happened on some plantations located in Hainan province,such as Danzhou,Baisha,Ledong,Baoting,Tunchang and so on.The bark of infected rubber trees became ridgy and brown,and then the latex flowed out.The twig died back and the whole plant died under serious condition.This paper carries on the investigations of rubber tree stem canker in the main rubber planting area of Hainan.We collected samples,isolated and identified the pathogen of this disease.In addition,the biological characteristics and molecular detection of the pathogen were studied.We also screened fungicides indoor in order to control this disease in the field.The main results are as follows:From 2014 to 2016,five surveys of rubber tree diseases were carried out on 23 rubber tree plantation farms in Hainan.The stem canker disease was widely happened on the 21 plantations among them and 79 samples with stem canker sympotom were collected.Then 63 fungal isolates were collected from the materials and classified into four categories:Fusarium solani,F.oxysporum,F.proliferatum and F.equiseti.The separation rate of F.solani was the highest,reach to 66.6%.Pathogenicity assays were performed on the stems of ruuber tree by four methods,which were agar plug with fungal mycelium inoculated on wounded detached stem,agar plug with fungal mycelium inoculated on wounded living stem,agar plug with fungal mycelium inoculated on wounded living stem which bark was cutted by the knife,conidial suspensions inoculated on wounded living stem.The results showed that the pathogenicity of F.solani was strongest and the symptoms which were similar to those of field was only recovered by agar plug with fungal mycelium inoculated on wounded living stem.On the base of the sequence analysis of rDNA-ITS and EF-l?,the main pathogen of rubber tree stem canker was identified as Fusarium solani.Meanwhile,we compared the nucleotide sequences of ITS regions of F.solani with other Fusarium strains.Then,a pair of specific primers QL-1F/QL-1R were designed in ITS of F.solani according to the polymorphism region,which can amplified a specific band from the F.solani genomic DNA.It can be used to specifically detect the F.solani from inoculated stems of rubber tree and stems of rubber tree stem canker in field.The sensitivity of the molecule detection can be improved when used the specific primers and ITS1/ITS4 primer together.F.solani strain HHNBSOlwas selected to study biological characteristics.The results showed that the optimum condition for mycelia growth of the strain included PD A medium,30 ?,pH 6,surose as carbon resource and potassium nitrate as nitrogen resource.The best condition for conidia production was Czapek medium,15 ?,pH 6,complete dark,D-xylose as carbon resource and ammonium oxalate as nitrogen resource.30?,pH 7,complete light,glucose or maltose as carbon source and ammonium oxalate as nitrogen source were the suitable condition for the germination of conidia.The toxicities of thirteen fungicides on F.solani were assayed in the laborary.The results indicated that the inhibitoty effect of fludioxonil was the strongest with EC50 valueof 0.0804mg/L,followed by carbendazim and prochloraz-manganese chloride complex and flusilazole.Mixtures of carbendazim and prochloraz-manganese chloride complex in ratio of 4:1,2:1,1:1,1:2 and 1:4 were tested.The results showed that all of the mixtures had better inhibition effect against F.solani,the ratio of 1:4 was the best inhibition effect among them with the SR of 2.8885.We recommend the screened fungicides to some farms to control this disease,which effect was fine. |
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